Electrochemical science advances最新文献

The use of microfluidic electrochemical reactors has been introduced several decades ago, but their application in the field of wastewater treatment is more recent (2010). The parallel development of electrochemical advanced oxidation processes (EAOPs) as promising technologies for effluent treatment make them good candidates to be implemented as thin film cells. This allows favoring the mass transfer, which is particularly interesting for heterogenous electro-oxidation. Moreover, the energy requirement is reduced, while there is possibility to treat low-conductivity solutions. This review intends to provide instructions on the main operating parameters to be optimized during the EAOPs treatment. Directions on engineering aspects have been given to overcome the main drawbacks of microreactors, such as fouling, scaling, and low treatment capacity, based on recent encouraging results given in literature. The promising development of hybrid processes that combine electroseparation with electroconversion would also benefit from such reactor designs.

Commercial-scale generation of carbon-containing chemicals and fuels by means of electrochemical CO₂ reduction (CO₂R) requires electrolyzers operating at high current densities and product selectivities. Membrane-electrode assemblies (MEAs) have been shown to be suitable for this purpose. In such devices, the cathode catalyst layer controls both the rate of CO₂R and the distribution of products. In this study, we investigate how the ionomer-to-catalyst ratio (I:Cat), catalyst loading, and catalyst-layer thickness influence the performance of a cathode catalyst layer containing Ag nanoparticles supported on carbon. In this paper, we explore how these parameters affect the cell performance and establish the role of the exchange solution (water vs. CsHCO₃) behind the anode catalyst layer in cell performance. We show that a high total current density is best achieved using an I:Cat ratio of 3 at a Ag loading of 0.01–0.1 mg_Ag/cm² and with a 1.0 M solution of CsHCO₃ circulated behind the anode catalyst layer. For these conditions, the optimal CO partial current density depends on the voltage applied to the MEA. The work also reveals that the performance of the cathode catalyst layer is limited by a combination of the electrochemically active surface area and the degree to which mass transfer of CO₂ to the surface of the Ag nanoparticles and the transport of OH⁻ anions away from it limit the overall catalyst activity. Hydration of the ionomer in the cathode catalyst layer is found not to be an issue when using an exchange solution. The insights gained allowed for a Ag CO₂R MEA that operates between 200 mA/cm² and 1 A/cm² with CO faradaic efficiencies of 78–91%, and the findings and understanding gained herein should be applicable to a broad range of CO₂R MEA-based devices.

A new dipping robot is presented for the execution of layer-by-layer (LbL) deposition procedures for the modification of electrode surfaces. It is composed of low-budget parts broadly available three-dimensional (3D) printer. New extra hardware components produced by 3D printing and the open-source software can turn such a device into a flexible dipping robot. The required changes in code as well as the printing instructions for the changed hardware components are documented and are made freely available together with tools that allow customizing LbL coating processes. The potential of this very flexible instrumentation is exemplified by a redox-active film of nickel hexacyanoferrate on a gold electrode modified by a monolayer of 3′-mercaptobiphenyl-carbonitrile. Scanning electron microscopy confirm the absence of micometer-sized cracks. It shows the typical voltammetric behavior of that material.

Practical interest in oxygen reduction reaction (ORR) has traditionally been due to its application at fuel cells’ cathode following its complete 4e route to the water. In search of new electrode materials, it was discovered that conducting polymers (CPs) also are capable of driving ORR, though predominantly halting the process at 2e reduction leading to hydrogen peroxide generation. As alternative ways to produce this “green oxidant” are attracting increasing attention, a detailed study of the ORR mechanism at CP electrodes gains importance. Here, we summarize our recent theoretical work on the topic, which underscores the fundamental difference between CP and electrocatalytic metal ORR electrodes. Our insights also bring to us the attention of outer-sphere electron transfer, not unknown but somewhat ignored in the field. We also put the action of CP electrodes in a more general context of chemical ORR and redox mediation responsible for the electrocatalytic ORR mechanism.

Room-temperature ionic liquids (ILs) have gained considerable attention as an important addition to conventional electrolytes because they exhibit large electrochemical windows and can reduce existing overpotentials in electrocatalysis. For the interfacial electrochemistry of ILs, a comprehensive understanding of molecular ions and the resulting electric double-layer structures as a function of electrode potential is mandatory, but the structures are largely different from conventional electrolytes. For that reason, we have studied the interfaces of Pt(111) in contact with ILs using 1-butyl-3-methylimidazolium [BMIM] and 1-butyl-2,3-dimethylimidazolium [BMMIM] cations as well as bis(trifluoromethylsulfonyl)imide [NTf₂] anions. We applied vibrational sum-frequency generation (SFG), where we interrogate vibrational bands from interfacial cations, anions, as well as interfacial water in situ and under potential control. Structuring of [NTf₂] anions and H₂O with electrode potential show hysteresis while a strong Stark tuning was absent. This indicates that the IL ions are oriented in the vicinity of the interface, without being directly adsorbed to the Pt(111) surface. Using the C-H stretching band from CH groups at the imidazolium ring, the ring reorientation with electrode potential was qualitatively determined. The imidazolium ring reorients as a function of potential from a more parallel orientation to an upright orientation with respect to the interfacial plane. This leads to the formation of voids in the layered structure of ions at the interface, which can be then filled with H₂O as evidenced by an increased SFG intensity from O-H stretching modes that are attributable to hydrogen-bonded interfacial water. Comparing the responses of the ILs, particularly of [BMMIM][NTf₂], shows a compact structure and a significantly pronounced rearrangement of the imidazolium ring that can also facilitates better incorporation of H₂O and significantly affects the reorientation of [NTf₂] anions and, thus, causes a pronounced hysteresis with electrode potential.

Porous electrodes are fast emerging as essential components for next-generation supercapacitors. Using porous structures of Co₃O₄, Mn₃O₄, α-Fe₂O₃, and carbon, their advantages over the solid counterpart is unequivocally established. The improved performance in porous architecture is linked to the enhanced active specific surface and direct channels leading to improved electrolyte interaction with the redox-active sites. A theoretical model utilizing Fick's law is proposed, that can consistently explain the experimental data. The porous structures exhibit ∼50%–80% increment in specific capacitance, along with high rate capabilities and excellent cycling stability due to the higher diffusion coefficients.

Electrochemical reduction of CO₂ in traditional aqueous electrolytes suffers from low faradaic efficiency towards desired products which can be traced back to low CO₂ solubility and strong competition from the hydrogen evolution reaction. The use of non-conventional electrolytes aims to mitigate these issues. This review will give a focused overview summarizing some of the most recent contributions on the electrochemical conversion of CO₂ in organic solvents, ionic liquids, solid electrolytes, and brines. We summarize the findings in terms of activity, selectivity, and durability for each of the systems. In addition, it provides an outlook about the role of water, cations, and anions in the reaction. We also highlight the challenges of the electrochemical reduction of CO₂ in each of the electrolytes. All the studies referred to in this review contribute meaningfully to reaching the technical targets for CO₂ electrolyzers in non-conventional electrolytes.

The number of publications on the electrochemical analysis of liquids increases year by year. The growth of publication activity is largely due to the development of new biosensors and the introduction of nanomaterials into the practice of electrochemical analysis. It is not the task of the author to review the entire array of publications, since the basic principles of electrochemical analysis in most publications remain practically unchanged. The purpose of this critical review is to find answers to two important questions for the development of electroanalysis. First, are all of the used electrochemical methods providing a measurement in the strict metrological sense of this term? That is, do they provide the necessary accuracy, validity, reliability, and reproducibility of the measurement results? Secondly, is electroanalytics capable of meeting the challenge of the information revolution by significantly increasing the information efficiency of each individual measurement? To answer these questions, we will identify the main sources of sensor signal noise by considering the electrochemical sensor as the primary decoder of “chemical information” into an analytical signal. Then we will evaluate the information efficiency of various measurement methods by using the approach of thermodynamics of information processes and considering a sensor as an open thermodynamic system.

Four mesoporous carbons (MCs) with tunable pore size were synthesized by soft template synthesis, employing a resorcinol-formaldehyde resin as a carbon precursor and a polyethylene oxide-block-polystyrene block copolymer as a sacrificial template in which the length of the polystyrene block (165, 300, 500, and 1150 units) allowed the modulation of the surface area of MCs (567, 582, 718 and 840 m² g⁻¹, respectively). The complete set of MCs was also doped with nitrogen by ball milling in the presence of cyanamide and stabilized in a second thermal treatment at 750°C, leading to nitrogen content of ∼2.65% in all samples. The two sets of MCs were used for evaluating both the effect of textural properties and nitrogen doping in the electrochemical reduction of oxygen in acid electrolytes. Each catalyst was characterized by means of elemental analysis and N₂ physisorption analysis, whereas the selected series of samples were also characterized by transmission electron microscopy, scanning electron microscopy, X-ray photoemission spectroscopy, inductively coupled plasma mass spectroscopy (ICP-MS), and Raman analysis. Voltammetric rotating ring-disk measurements in 0.5 M H₂SO₄ demonstrated that the catalytic activity for the O₂ reduction scales with the surface area in the non-doped series, and also the selectivity for the two-electron process leading to H₂O₂ increases in the samples having wider pores and higher surface area, even if the leading mechanism is the tetraelectronic process leading to H₂O. The doping with nitrogen leads to a general increase of the catalytic activity with a shift of the O₂ peak potential to more positive values of 75–150 mV. In the doped series, nitrogen doping prevails on the textural properties for guiding the selectivity toward the two- or four-electron process, since a similar H₂O₂ yield was observed for all N-MC samples. The possible presence of FeN_x sites derived from the ball milling fixation of nitrogen was evaluated by using the NO-stripping technique.

Ubiquinone (UQ) is a lipophilic compound present in most living organisms, where UQ's interesting but complex electrochemistry serves an important role in the transfer of electrons and protons within and across the mitochondrial membrane. We briefly review the electrochemical characteristics of UQ and its reduced state, ubiquinol, in solution and immobilized on electrodes, together with its application in electrochemical sensing and detection systems, for example, measuring redox status with reference to reactive oxidative species. The importance of the local environment, solvent, electrolyte, organic membrane, and pH, on the electrochemical behavior of UQ, is also discussed. We discuss techniques used for the direct detection of UQ such as liquid chromatography-electrochemistry. Mediated electrochemistry of UQ allows for quantitative measurements of ions, small molecules, and other analytes such as glucose via chemical sensors and biosensors.